FIG. 1 shows a schematic diagram illustrating the structure of a general color cathode ray tube. As shown in FIG. 1, the color cathode ray tube generally includes a glass envelope having a shape of bulb and being comprised of a faceplate panel 1 to which explosion prevention means is fixed, a tubular neck, and a funnel 2 connecting the panel 1 and the neck. A phosphor screen 4 is formed on the inner surface of the faceplate panel 1. The phosphor screen 4 is B130 coated by phosphor materials of R, G, and B.
A multi-apertured color selection electrode, i.e., shadow mask 3 is mounted to the panel 1. The shadow mask 3 is hold by a peripheral frame 9. An electron gun 11 is mounted within the neck to generate and direct electron beams 6 along paths through the mask to the panel 1.
The cathode ray tube further comprises an inner shield 10 for shielding the tube from external geomagnetism. The inner shield 10 is joined to the frame 9. Further, a spring 7 for combining the frame 9 and the funnel 2 is joined to the frame 9.
FIG. 2a shows a cross-sectional view illustrating the conventional cathode ray tube and FIG. 2b shows a cross-sectional view illustrating a cathode ray tube of slim type.
As shown in FIGS. 2a and 2b, the cathode ray tube has a panel portion 21, a body portion of the funnel 22, a yoke portion of the funnel 23 and a neck portion. Hereinafter, the following parameters are used to describe the prior art and the present invention.
The panel portion 21 is a portion from an outer surface of the panel 1 to a seal line plane (SL) 24. The body portion of the funnel 22 is a portion from the SL 24 to a yoke line plane (YL) 25. The yoke portion of the funnel 23 is a portion from the YL 25 to a neck line plane (NL) 27.
Herein, deflection axis X means extension line of the central axis of the electron gun through the screen.
Deflection center C-means a point on the deflection axis X such that deflection angle made with the deflection axis X and a line which connects the deflection center C and a diagonal end of the effective screen becomes maximum.
Deflection center C means a point on the deflection axis X such that deflection angle made with the deflection axis X and a line which connects the deflection center C and a diagonal end of the effective screen becomes maximum.
Deflection angle means an angle made with the deflection axis X and a line connecting the deflection center C and a diagonal end of the effective screen.
The seal line plane SL is a vertical plane which is perpendicular to the deflection axis X and includes a closed line through which the panel and the funnel is sealed together.
The yoke line plane YL means a vertical plane which is perpendicular to the deflection axis X and includes a boundary line between the body and yoke portions of the funnel.
The neck line plane NL means a vertical plane which is perpendicular to the deflection axis X and includes a closed line through which the neck portion and the funnel is sealed together.
A reference line plane RL means a vertical plane which is perpendicular to the deflection axis X and includes the deflection center C.
In general, the volume and weight of the cathode ray tube is lager than the other display apparatuses. Therefore, the conventional cathode ray tube has been changed into slim type.
It is preferable to reduce the body portion of the funnel 22 to make the cathode ray tube to be slim type as shown in FIG. 2b. However, the reduction of the body portion of the funnel 22 has the following problem.
The electron beams 6 of the cathode ray tube of slim type have to be scanned with larger deflection angle (θ-θ′) than the conventional one.
For example, the conventional cathode ray tube has the deflection angle which is less than 100°. On the other hand, the cathode ray tube of slim type has the deflection angle of larger than 100°. As the depth of the cathode ray tube decreases, the electron gun becomes closer to the panel 1. Therefore, larger deflection angle (θ′) is required.
Moreover, the reduction of depth of the cathode ray tube is one of causes increasing the stress of the panel glass. If the stress increases, the strength of structure of cathode ray tube becomes weak such that the cathode ray tube is easily exploded by external shock. The portion which is most weak against external shock is the portion adjacent to YL 25.
Therefore, the funnel 2 is easily destroyed during impact test. The cathode ray tube having the minimum weight is economical, but it must satisfies the stress and stability at the same time.
According to Korean Laid-open Patent Publication No. 2001-110113, the depth of the body potion of the funnel was designed to be small to reduce the weight of the cathode ray tube, and a rib was fixed on the body potion of the funnel to reinforce the strength. However, it was not enough that stand against a vacuum stress.
Hereinafter, the manufacturing process of general cathode ray tube is described shortly, and the influence of vacuum and compressive stress during the manufacturing process is described.
The manufacturing process of general cathode ray tube divides into a preceding process and a later process. The preceding process is the process forming the phosphor screen on the inner surface of the faceplate panel, and the later process is made up the following process.
Firstly, a sealing process joining the panel formed the phosphor screen and mounted the shadow mask assembly to the funnel formed a frit at the sealing surface is progressed. After this, an encapsulation process inserting the electron gun into the neck portion of the funnel, making the inside of cathode ray tube vacuous through a ventilating process, injecting a gas, and sealing up the hole for the ventilation and the vacuum is progressed.
Where, the inside of the glass of the cathode ray tube is regulated in the vacuum state of 10-7 Torr at the ventilating process such that the movement of the electron beams become higher.
But, as above, when the inside of the glass is the vacuum state, the tensile stress and compressive force apply to each region the inside and outside of the cathode ray tube.
Namely, the panel 1 and the funnel 2 are received the vacuum stress by an atmospheric pressure, and particularly, the cathode ray tube of slim type receives more the force per the unit area than the general cathode ray tube because the total length of the panel 1 and the funnel 2 get to be small.
FIG. 3 shows a schematic view illustrating the tensile stress and the compressive stress of the inside of a general cathode ray tube in the vacuum state. A dotted line shows the compressive stress and a solid line shows the tensile stress. The tensile stress and compressive stress is important factor in a viewpoint of an impact resistance.
In case that the glass receives the heavy external shock, the glass is cracked, and if the crack is infinitely progressed in a brief instant the glass is completely broken. In other words, the surface of the glass is received the tensile stress which progress the crack, and the glass is completely broken or the surface of the glass is occurred many crack after all.
On the other hand, as the compressive stress preferably prevents from the progress of the crack, as shown in FIG. 3, the center portion of the panel is strong and the corner portion of the panel is weak at the external shock.
Moreover, as the direction of the axis is received the compressive stress and the direction of the diagonal axis is received the tensile stress at the yoke portion of the funnel, its portion may be broken by a little shock.
FIG. 4a shows a part of high tensile stress of a general cathode ray tube and FIG. 4b shows a part of high tensile stress of a cathode ray tube of slim type.
As shown in FIGS. 4a and 4b, in case of the general cathode ray tube, a stress concentration is generated at the corner portion {circle around (1)} of the panel 1 and in case of the cathode ray tube of slim type, a stress concentration is generated at the YL portion {circle around (3)} adjoined the body portion of funnel and the yoke portion of the funnel.
FIG. 5 shows a simulating view illustrating the occurrence of a tensile stress of a YL portion inside according to making into a slim and a decrease of an over-all length. As shown in FIG. 5, the tensile stress is concentrated upon the YL portion 25.
To solve above problems, the following methods may are considered, but exist the following problems.
The method increasing the thickness of the glass may be considered. However, this method has the problem which the electron beams are bumped against the inner surface of the yoke portion the image and a shadow is cast on a screen.
And the method attaching a reinforcing band to the sidewall portion of the panel to prevent the cathode ray tube from being exploded by external shock may be considered, but the effect is weak in the cathode ray tube of slim type.
Moreover, the methods using a tempered glass applied heat treatment or adhering a film on the surface of the panel to increase a physical strength may are considered. However, these methods are applied to the panel and can not applied to the glass.
Therefore, the characteristic of the electron gun and the deflection yoke should be improved and particularly, the problem of a high strength of the glass should be solved before everything else to embody the cathode ray tube of slim type.